The present invention relates to a method of photochemically treating the surface of a material such as a semiconductor substrate by utilizing radiation energy to form a thin film on the surface with the precision of atomic scale, or one or a few atomic (or molecular) layers of the surface are removed to etch the surface, and more particularly to a method of photochemical surface treatment suitable for use in the case where a thin film having a predetermined pattern is formed on the above surface or the surface is etched to a predetermined pattern.
The so-called atomic layer epitaxy for depositing one or a few atomic (or molecular) layers repeatedly on a substrate to form a film is a very excellent technique capable of producing a thin film having a good crystalline quality. As described on pages 516 to 520 of the June 1984 issue of the OHYOH BUTURI (the proceeding of the Japan Society of Applied Physics), the following surface treatment is carried out in the conventional atomic layer epitaxy. A first gas is introduced into a chamber in which a substrate maintained at a predetermined temperature is disposed, and then the chamber is evacuated to leave the one molecular layer (namely, the first molecular layer) of gas molecules adsorbed on the surface of the substrate. Thereafter, the second gas (or the first gas) is introduced into the chamber and then the chamber is again evacuated, to form the second molecular layer on the first molecular layer or to form the third molecular layer on the surface of the substrate as a result of the reaction of the second molecular layer with the first molecular layer. By repeating the above process, a film can be formed on the substrate with the precision of atomic scale. However, it is required to carry out the introduction of gas into the chamber and the evacuation of the chamber alternately and repeatedly, and hence the conventional atomic layer epitaxy has a drawback that a thin film cannot be grown at high speed. Further, the above epitaxy has another drawback that it is impossible to selectively grow a thin film only on the predetermined material forming a pattern on the substrate.